Re: [PATCH v3 0/4] Split page_type out from mapcount

[Matthew Wilcox]

On Thu, Mar 01, 2018 at 03:44:12PM +0300, Kirill A. Shutemov wrote:
> On Thu, Mar 01, 2018 at 08:17:50AM +0100, Martin Schwidefsky wrote:
> > Yeah, that is a nasty bit of code. On s390 we have 2K page tables (pte)
> > but 4K pages. If we use full pages for the pte tables we waste 2K of
> > memory for each of the tables. So we allocate 4K and split it into two
> > 2K pieces. Now we have to keep track of the pieces to be able to free
> > them again.
> 
> Have you considered to use slab for page table allocation instead?
> IIRC some architectures practice this already.

You're not allowed to do that any more.  Look at pgtable_page_ctor(),
or rather ptlock_init().